diff options
Diffstat (limited to 'Demo')
| -rw-r--r-- | Demo/threads/sync.py | 55 |
1 files changed, 51 insertions, 4 deletions
diff --git a/Demo/threads/sync.py b/Demo/threads/sync.py index 53ef28e..4e99979 100644 --- a/Demo/threads/sync.py +++ b/Demo/threads/sync.py @@ -4,6 +4,7 @@ # condition() # a POSIX-like condition-variable object # barrier(n) # an n-thread barrier # event() # an event object +# semaphore(n=1)# a semaphore object, with initial count n # # CONDITIONS # @@ -35,7 +36,7 @@ # threads are .wait'ing, this is a nop. # # Note that if a thread does a .wait *while* a signal/broadcast is -# in progress, it's guaranteeed to block until a subsequenct +# in progress, it's guaranteeed to block until a subsequent # signal/broadcast. # # Secret feature: `broadcast' actually takes an integer argument, @@ -184,8 +185,30 @@ # see the event get around to .wait'ing on it. But so long as you don't # need to .clear an event, events are easy to use safely. # -# Tim Peters tim@ksr.com -# not speaking for Kendall Square Research Corp +# SEMAPHORES +# +# A semaphore object is created via +# import this_module +# your_semaphore = this_module.semaphore(count=1) +# +# A semaphore has an integer count associated with it. The initial value +# of the count is specified by the optional argument (which defaults to +# 1) passed to the semaphore constructor. +# +# Methods: +# +# .p() +# If the semaphore's count is greater than 0, decrements the count +# by 1 and returns. +# Else if the semaphore's count is 0, blocks the calling thread +# until a subsequent .v() increases the count. When that happens, +# the count will be decremented by 1 and the calling thread resumed. +# +# .v() +# Increments the semaphore's count by 1, and wakes up a thread (if +# any) blocked by a .p(). It's an (detected) error for a .v() to +# increase the semaphore's count to a value larger than the initial +# count. import thread @@ -306,10 +329,34 @@ class event: def wait(self): self.posted.acquire() - while not self.state: + if not self.state: self.posted.wait() self.posted.release() +class semaphore: + def __init__(self, count=1): + if count <= 0: + raise ValueError, 'semaphore count %d; must be >= 1' % count + self.count = count + self.maxcount = count + self.nonzero = condition() + + def p(self): + self.nonzero.acquire() + while self.count == 0: + self.nonzero.wait() + self.count = self.count - 1 + self.nonzero.release() + + def v(self): + self.nonzero.acquire() + if self.count == self.maxcount: + raise ValueError, '.v() tried to raise semaphore count above ' \ + 'initial value ' + `maxcount` + self.count = self.count + 1 + self.nonzero.signal() + self.nonzero.release() + # The rest of the file is a test case, that runs a number of parallelized # quicksorts in parallel. If it works, you'll get about 600 lines of # tracing output, with a line like |